A series of peptides will be synthesized and tested as substrates for the vitamin K-dependent rat liver microsomal carboxylase. The activity of all compounds will be compared to that of Phe-Leu-Glu-Glu-Leu which has been shown to be a good substrate for the enzyme. During the next year, specific compounds to be synthesized include those where D-Glu is substituted for L-Glu; and, when L-Glu is replaced with L-Homoglutamic acid, the cyclic peptide corresponding to residues 18-23 of prothrombin will also be synthesized, as will peptides which contain Glu residues that have been derivatized at the gamma-carbon of the Glu residue. All peptides will be assayed for both substrate and inhibitor activity.